In the case of cylinder heads for internal combustion engines powered with diesel fuel, particularly in the case of direct fuel injection engines, the combustion chamber region does not have dome-shaped geometry, as is usually the case with cylinder heads for petrol engines, but is incorporated evenly into the equally flat sealing surface, by which the diesel cylinder head rests in the installed state against the sealing surface, associated therewith, of the respective engine block. The combustion chamber region of the cylinder head in this way lies in the sealing plane of the engine block.
In order to be able to produce the sealing surface with the precision necessary for a permanently assured tight seat, in the case of the unfinished cylinder head casting, a machining allowance, which is removed during finishing of the cylinder head, is usually pre-cast. In practice the additional thickness of the section, carrying the sealing surface, of the unfinished cylinder head casting, provided as machining allowance and removed in the course of finishing usually amounts to 2 mm-3 mm. The mechanical removal of this thickness enables the sealing surface to be produced with extreme precision and the necessary evenness.
In service the combustion chamber region of the cylinder head is loaded to the maximum due to the high pressures and high temperatures arising in the case of diesel engines. This load, in particular with cylinder heads cast from light metallic alloys, on the valve seats and valve crosspieces usually incorporated in their combustion chamber regions, leads to increased crack susceptibility. This susceptibility is particularly problematic under consideration of the desire for cylinder heads with even higher load-bearing capacity, which on the part of the manufacturers and users of diesel engines is greater in view of the requirement for as much power output as possible.
Just at the time when the cylinder heads are to be made of a light alloy material, for example an aluminum alloy, these demands have only been able to be met till now with substantial technical effort as regards the alloy, design or production. Thus the load-bearing capacity of the valve seats in the region of the combustion chamber can be improved for example by incorporating elements made of metal with higher load-bearing capacity in the casting. The effort linked with incorporating the valve seats in the casting and the measures necessary for their sufficiently solid integration in the light alloy of the cylinder head however entails additional production costs. The same applies to the possibility of increasing the strength and elongation properties of the combustion chamber region by additional heat treatment.